Apparatus for converting molten thermoplastic in cup-like articles

ABSTRACT

Thermoplastic melted and pressurized in a conventional extruder is confined in and forced through a heated tube to form a molten viscous stream from which globs of accurately measured volumes are cut off successively, immediately deposited one by one into an open mold and converted into a thin walled cup in the telescoping of male and female dies which, when fully closed, define a cavity corresponding precisely in volume and shape to the cup. The dies are mounted in a flywheel actuated press and, after receiving each glob, are closed immediately and rapidly with enough propelling energy to subject the glob, in the final closing of the mold, to an impact of sufficient magnitude to first spread the plastic across the bottom of the cavity, then force an upward flow through the thin side wall thereof and finally into the bead part of the cavity so as to fill and preferably overflow the latter. The dies are maintained below the solidification temperature of the plastic and are held closed long enough in each cycle to insure cooling and solidification of the plastic for retention of the cavity shape and easy ejection of each cup formed in the extremely short cycles of the molding press.

United States atet Foster FOREIGN PATENTS OR APPLICATIONS APPARATUS FOR CONVERTING MOLTEN THERMOPLASTIC IN CUP- LIKE ARTICLES John A. Foster, Rockford, Ill.

Assignee: J. L. Manufacturing Co., Rockford,

Filed: Dec. 28, 1970 Appl. N0.: 101,926

Inventor:

Related U.S. Application Data Continuation-in-part of Ser. No. 789,183, Jan. 6, I969, abandoned.

US. Cl. ..425/4l2, 425/145, 425/416 Int. Cl ..B29c 3/00 Field of Search ..l8/34 M, 42 MP; 164/155;

References Cited UNITED STATES PATENTS 3/1959 Austria 1 8/42 D 1 Sept. 19, 1972 Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[5 7] ABSTRACT Thermoplastic melted and pressurized in a conventional extruder is confined in and forced through a heated tube to form a molten viscous stream from which globs of accurately measured volumes are cut off successively, immediately deposited one by one into an open mold and converted into a thin walled cup in the telescoping of male and female dies which, when fully closed, define a cavity corresponding precisely in volume and shape to the cup. The dies are mounted in a flywheel actuated press and, after receiving each glob, are closed immediately and rapidly with enough propelling energy to subject the glob, in the final closing of the mold, to an impact of sufficient magnitude to first spread the plastic across the bottom of the cavity, then force an upward flow through the thin side wall thereof and finally into the bead part of the cavity so as to fill and preferably overflow the latter. The dies are maintained below the solidification temperature of the plastic and are held closed long enough in each cycle to insure cooling and solidification of the plastic for retention of the cavity shape and easy ejection of each cup formed in the extremely short cycles of the molding press.

4 Claims, 34 Drawing Figures PATENTEDSEP 19 I972 SHEET UBUF 11 QJOhl b a," 3 VJQWWJ CR TTO RNDEDQ/ PATENTED 3.692 456 SHEET 0m 11 A7 ut gjohio gz f r PATENTED 19 3.692.456 SHEET 10 OF 11 APPARATUS FOR CONVERTING MOLTEN THERMOPLASTIC IN CUP-LIKE ARTICLES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 789,183, filed Jan. 6, 1969, now abandoned.

BACKGROUND OF THE INVENTION In the past, tubular articles such as tubes. and cups with or without a lip bead and composed of thermoplastic material have been formed commercially by injection molding, that is, forcing free flowing plastic into a closed mold through a centrally located orifice, thermal forming by drawing or forcing areas of a softened sheet into or onto an inner or outer contoured die surface, or by blowing up a tubular parison. Each of these processes is subject to one or more inherent and well recognized limitations including prolonged cycle time for cooling and solidification, excessive and nonuniform wall thickness, waste of material, costly trimming, high stressing and weakening at gates and thin sections, etc. In compression molding, powdered or granular plastic material is compressed between heated dies in the slow closing of a mold is limited to thermosetting materials.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a new and improved apparatus by which all of the above disadvantages are eliminated and thermoplastic cup-like articles of substantial depth may be formed at substantially lower cost, in shorter press cycles, with substantially thinner side walls of uniform thickness, with very little scrap, and, when desired, with a bead of solid cross-section around the container lip.

Generally stated, the invention involves the use of a mold comprising male and female dies having opposed surfaces which, when the mold is fully closed, define a closed cavity having the precise shape of and a volume closely corresponding to the cup or similar article to be formed. The thermoplastic is melted and pressurized outside of the mold and delivered in a continuous stream from a conventional extruder and, without substantial surface cooling of the stream, globs of accurately measured volumes slightly greater than the mold cavity are cut off successively from the leading end of the advancing stream and deposited immediately into the open mold. The latter is closed immediately with sufficient rapidity and adequate propelling energy quickly available from a suitable source to compress the glob between the bottom walls of the male and female dies and, before the plastic has time to cool and solidify by contact with the cavity walls, force the plastic to flow radially across the bottom, then upwardly through the cavity side wall, and finally completely fill the lip forming portion of the cavity, any excess volume overflowing to leave a continuous and easily separable flash ring. While various kinds of energy sources may be employed to apply the necessary compressive force to the molten glob of plastic at least in the final part of the molding closing, the energy stored in a rotating flywheel is utilized in the present instance.

In an improved form of the invention, each molten glob is injected into the mold cavity through a passage extending axially through the stationary one of the dies while the opposed ends are separated, the glob thus being centered in the bottom of the mold cavity thus facilitating uniform flow of the plastic first outwardly across the cavity bottom and then upwardly through the side wall. During the final closing of the mold, the end of the plunger by which the glob is injected into the mold is flush with the bottom of the stationary die and thus forms part of this die.

In both of the forms disclosed, the dies are maintained at a temperature substantially lower than the softening point of the plastic and are held closed for an interval long enough to insure adequate cooling for complete solidification of the plastic and easy removal of the container from the dies as the latter are opened, the flash ring being later broken or trimmed off from the cup lip.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a cup embodying the novel features of the present invention.

FIG. 2 is a section taken along the line 2-2 of FIG. 1.

FIGS. 3 through 11 are vertical cross-sections showing different positions of the molding dies in the course of converting a glob of thermoplastic into the cup shown in FIGS. 1 and 2.

FIG. 12 is a fragmentary front elevational view of the improved molding apparatus with some of the parts shown schematically for the sake of completeness.

FIG. 13 is a fragmentary side elevation of the molding press with parts broken away and shown in section taken along the line l3l3 of FIG. 12.

FIG. 14 is a fragmentary section taken along the line 14-14 ofFIG. 13.

FIG. 15 is a fragmentary section taken along the line 15-15 of FIG. 14.

FIG. I6 is an enlargement ofa part of FIG. 15.

FIG. 17 is a fragmentary section taken along the line l7--l7 of FIG. 15 showing the parts in different positions.

FIG. 18 is a perspective view of the cup as ejected from the molding press.

FIG. 19 is an exploded perspective view of the flash ring and the cup after trimming.

FIGS. 20 and 21 are fragmentary sections taken along the line 2020 of FIG. 13 showing different positions of the parts.

FIGS. 22 and 23 show a part of FIG. 13 with the crank in different positions.

FIG. 24 is a chart showing the timing of the motions involved in forming the globs and converting the same into cups.

FIG. 25 is a perspective view similar to FIG. I showing a modified form of cup.

FIG. 26 is a fragmentary cross-section like FIG. 15 showing the die setup for molding the modified cup. FIG. 27 is a fragmentary and schematic view of an improved apparatus for practicing the present invention.

FIG. 28 is a fragmentary perspectiveview of a part of FIG. 27.

FIG. 29 is a fragmentary section taken along the line 29-29 of FIG. 27.

FIG. 30 is a section taken along the line 3030 of FIG. 29.

FIG. 31 is a fragmentary cross-section similar to FIG. 5 with the dies approaching closed position.

FIG. 32 is a similar view with the dies fully closed.

FIG. 33 is a view similar to FIG. 29 with the parts in different positions.

FIG. 34 is a chart of the timing of the motions of the parts shown in FIGS. 27 to 33.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of illustration, the invention is shown in the drawings in connection with conversion of successive globs (FIG. 3) of molten thermoplastic into cups 11 (FIGS. 1 and 2) comprising a slightly dished bottom 12 of uniform thickness, for example about 0.020 of an inch, a pedestal 13 depending from the periphery of the bottom, a side wall 14 of uniform thickness somewhat thinner than the bottom, for example 0.018 of an inch and diverging upwardly to and integral with a head 15 having rounded top and side surfaces 16 and 17 (FIG. 16) and providing a downwardly facing shoulder 18 around which a suitable cover (not shown) may be hooked and sealed against the top of the bead. In the present instance, the bead takes the form of a curl having a radial width several times the thickness of the side wall 14, the shoulder being defined by the free edge of the curl.

Most extrudable thermoplastic materials may be employed, polystyrene, polyethylene and polypropylene being examples. A preferred material is polystyrene sold by Dow Chemical under the trade designation of 495 which has a Vicat softening point of about 207 F. At the preferred molding temperature, this plastic is very viscous and relatively soft and a glob 10 thereof will not flow or sag appreciably when placed on a supporting surface.

For forming cups of the above character in accordance with the present invention, the globs may vary in shape so long as the volume of the plastic is equal to and preferably slightly greater than that of the cavity in which the cup is molded. With the mechanism herein shown, the globs for forming successive cups are quite uniform in shape and, in the embodiment shown in FIGS. 1 to 26, each is somewhat elongated and generally cylindrical with relatively square ends. In the modification illustrated in FIGS. 27 to 34, the globs as introduced into the mold cavity take the form of a relatively flat circular mass as shown in FIG. 29. The glob is free of surface crevices or folds which would interfere with the contemplated proper flow of the plastic through the mold cavity.

GLOB FORMATION To form the plastic globs, raw material is delivered into the hopper 20 of an extruder 21 (FIG. 12) 05 conventional construction, having a heater by which the plastic is melted and rendered sufficiently soft and pliable to be movable by a screw 22, pressurized, and discharge through the openings in an outlet plate 23 (FIG. 20) and into one end of a tube 28 by which the molten plastic is confined to form a continuously advancing stream 24. After starting the softening of the plastic, most of the needed heat is developed by friction in the extruding action. By manually adjusting a knob 24 or the like, the amount of heat delivered by the heater of the extruder may be adjusted to provide the desired temperature of the plastic as discharged from the extruder into the tube 28. As shown in FIG. 20, the flanged inlet end of the tube 28 is clamped by a nut 29 to the extruder casing while the outlet end of the tube is suitably supported on the frame of the press in which the cup forming dies are mounted. When the Dow 49S plastic is used, an indicated temperature at the outlet of about 425 F. has been found to be suitable.

A motor 25 (FIG. 12) operates through suitable variable speed drive and reducing mechanism 26 to drive the extruded screw at a constant speed such that the molten plastic is discharged into the tube 28 at a pressure sufficient to advance the stream 24 from the extruder at a substantially constant rate. The latter may be varied usually by turning a hand wheel 27 or the like which acts through the mechanism 26 to enable the desired speed rate to be selected.

The tube 28 is several times as long as each of the globs 10 to be formed and preferably is composed of heat-conducting metal so that, by heating the tube to a proper temperature, all of the plastic stream is maintained at a temperature closely corresponding to the desired temperature of the glob mass at the time of delivery into the open mold. For this purpose, electric band heaters 30 (FIGS. 20 and 21) encircle the tube and are spaced along the latter while being suitably energized and heat insulated.

As shown in FIGS. 20 and 21, provision is made to compensate for variations in the rate of delivery of the molten plastic in the continuous operation of the extruder and for the interrupted flow at the end of the stream incident to cutting off the stream end to form the successive globs. To this end, an opening 31 in the side of the tube 28 is defined by the end of a tube 32 rigid with and extending transversely of the tube 28 and providing a cylinder 33 in which a yieldably loaded plunger 34 is adapted to slide back and forth. Herein, the loading is produced by compressed air delivered from a source 35 (FIG. 12) through an adjustable regulater 36 and exerted on the head end of a piston 37. The latter is slidable in a cylinder 38 and its rod 39 is an extension of the plunger 34. In the same manner as the tube 28, the tube 32 is maintained at the desired temperature by an electric band heater 4]. The cylinder 32 and the plunger 34 thus loaded form a hydraulic accumulator for receiving molten plastic from the tube 28 through the opening 31 when the pressure in the tube exceeds a predetermined value and for forcing the plastic back into the tube 28 in response to a decrease in pressure therein. If desired in order to shorten the length of each plastic glob 10 in the glob forming mechanism shown in FIGS. 20 and 21, the inner wall of the tube 28 at the outlet end portion thereof is increased in cross-section by forming the same with a diverging taper 42 preferably terminating in an enlarged cylindrical end portion 43.

The invention contemplates cutting off accurately measured lengths of the leading end of the advancing stream 24 successively to form the globs 10 while avoiding any substantial cooling of the stream up to the point of cut off. For these purposes and in the form shown in FIGS. 1 to 27, the outlet end 43 of the tube 28 communicates with a side opening 44 intermediate the ends of a tube 45 suitably supported on the frame of the molding press and extending transversely of the tube 28. One end portion projects horizontally toward the mold 46 in which the cups 11 are formed and defines a cylinder 47 in which a plunger 48 fits closely and is slidable back and forth between the retracted and advanced positions shown in FIGS. and 21. In the retracted position, the end opening 49 of the tube 45 is fully uncovered and molten plastic, propelled by the force applied by the accumulator piston 37 and the continuous force of the extruder screw, is forced beyond the tube end 44 and into the cylinder 47. The molten plastic, being flowable under pressure, assumes the cylindrical contour of the cylinder 47 and flows a short distance ahead of the opening 44 as shown in FIG. 20 before being cut off from the advancing stream as a piston 51 on the plunger 48 is propelled rapidly to the advanced position (FIG. 21) by the admission of compressed air from the source 35 to the head end of the piston cylinder 52.

Retraction of the plunger to the position shown in FIG. 20 occurs in response to closure of a switch 53 (FIG. 12) to energize a solenoid 54 for shifting a valve 55 to admit fluid from the pressure source 35 to the rod end of the cylinder 52. Similarly, closure of a switch 56 energizes a solenoid 57 to shift the valve 55 and admit pressure fluid to the head end of the cylinder 52 so as to cause the piston 51 and the plunger 48 to be propelled forwardly and rapidly to the position shown in FIG. 21. In this movement, the plunger end 58 moves across the opening 44 thus cutting off the mass of plastic then confined within the cylinder 47 and advancing this mass along the cylinder and out of the end 49 thereof. This end is disposed just above and just short of the near edge of the lip of the female die of the mold 46 as shown in FIG. 13. Preferably, and in the advanced position of the plunger 48, the end 58 thereof is disposed a short distance beyond the nozzle end 49 so as to overlie the edge of the lip opening of the die. The force applied by the piston 51 is sufficient to propel the glob partially across the lip opening as it is released from the nozzle and starts to fall into the recess of the female die. A coating of silicone or the like on the end 58 of the plunger facilitates release and falling of the molten glob into the die.

Electric band heaters 60 surrounding opposite end portions of the tube 45 maintain the desired temperature of the plunger 48 and the wall of the cylinder 47 while each successive glob is being formed in the cylinder ahead of the plunger end as well as during the projection of the glob through and out of the cylinder. By confining the plastic by rigid heated walls during its advance from the extruder outlet 23 and all the way to the point of its discharge from the cylinder 47 the desired molten condition and viscosity is maintained, and each glob will be heated uniformly throughout its mass as it is deposited in the open mold. Such confinement and the manner of forming each glob by flowing the plastic transversely into and across the cylinder 47 from the tube outlet 43 insures that each glob, as discharged from the nozzle 49, will be generally cylindrical and always free of crevices or folds likely to cause imperfections in the walls of the cup as finally molded.

While the plunger 48 is advanced from the retracted position shown in FIG. 21 and thus partially or fully covering the end 44 of the tube 28, the flow of molten plastic from the extruder continues and the resulting build-up in pressure overcomes the loading of the accumulator causing a flow out of the tube 28 and into the cylinder 33 against the pressure on the head end of the piston 37. Then, as the plunger 48 is retracted and uncovers the opening 44, the accumulated and increased pressure within the tube 32 is released and molten plastic in the cylinder 33 is forced back into the tube 28 and through the open end 44 into and across the cylinder 47. Formation of another of the globs 10 is thus initiated.

From the foregoing and, as illustrated in FIGS. 20 and 21, it will be apparent that during operation of the extruder and by periodic reciprocation of the cut-off plunger 48, the leading end portion of the stream 24 of molten plastic discharged continuously from the extruder will be cut off successively to form the molten globs 10 which, as delivered into the open mold, contain equal and accurately measured volumes of the plastic uniformly heated throughout each glob. The volume of plastic in each glob is determined by the rate of delivery of the molten plastic by the extruder and the period during which the opening 44 remains uncovered by the plunger 48 in each cup molding cycle with which the reciprocations of the piston 51 are timed closely. This may be achieved as shown by a power actuator activated in timed relation to the cycles of the molding press or alternatively the plunger 48 may be actuated by a suitable cam mechanism coupled mechanically to the driven shaft of the press.

MOLD CONSTRUCTION AND ACTIVATION The mold 46, in the form shown in FIGS. 12 to 15, includes an upwardly opening female die 61 which has a downwardly tapered internal surface 62 precisely contoured to the desired size and shape of the outer surface of the cup bottom 12 including the pedestal 13, the cup side wall 14, and the lip bead l5. Coacting with and interfitting with the female die is a male die 63having an external surface 64 similarly tapered and precisely contoured to correspond to the interior of the cup including the bottom, the side wall, and the lip 15. When the dies thus contoured are fully closed together as shown in FIGS. 8 and 15, the cavity 65 between their opposed surfaces will be shaped and of a volume corresponding precisely to that of the cup desired to be formed including the lip bead. Preferably, the dividing line between the dies when closed is located at the outermost periphery of the bead forming portion 71 (FIG. 7) of the die cavity this line being defined by opposed outtumed surfaces 66 and 67 at the bottom of a counterbore 68 in the upper open end of the female die and around a flange 69 at the base of the male die.

To accommodate slight variations in the volumes of the globs as delivered from the extruding and measuring setup above described and insure complete filling of the bead area 71, it is desirable to employ in each glob a volume slightly greater than the total volume of the die cavity 65 and provide, in the construction of the dies in the closed position thereof, an opening around the outer edge of the bead area 71 allowing for the escape of the excess'from the cavity. Herein, the vent opening is preferably a narrow gap, for example, .002 of an inch thick, remaining between the die surfaces 66 and 67 when the mold is fully closed. Around it outer periphery, the overflow gap communicates with an annular passage 70 defined by a groove in the bottom of the counterbore 68 coacting with the outer edge portion of the surface 67 on the male die. The amount of plastic in each glob in excess of the total volume of the cavity 65 is sufficient to insure some overflow outwardly around the full circumference of the bead area 71 and the resultant formation around the bead of the cup of a continuous and more or less frangible flash ring 72 (FIGS. 18 and 19) which may be broken or trimmed off easily after removal of the cup from the die.

Referring not to FIG. 15, the female die is a two-part cup including a ring 73 closely telescoped in and seated on a flange inturned from a cylindricai ring 74 and secured by screws 75 to the lower end of the ring 73. In the molding, the internal surface of the latter forms the underside surface of the lip bead or curl and the outer surfaces of the cup side wall and the pedestal 13. The inner surface of the pedestal and the bottom surface of the cup is formed by the peripheral and top surfaces on a disk 76 clamped by screws 77 against the flange of the ring 73 and having a stem 78 depending through the bottom of the ring 73 and a plate 79. The latter rests on and is anchored to the lower and stationary platen 81 of the molding press (FIG. 13).

The male die (See FIG. 15) is also formed in two parts, the outer one being a downwardly tapered cup 82 of substantially uniform thickness and with the outer surface 64 shaped to form the top and outer periphery of the lip bead 15, the inner surface of the side wall of the plastic cup and the outer portion of the top of the cup bottom 12. The remainder and central part of the cup bottom surface is formed by the downwardly rounded surface of an ejector head 83 which is seated in a frusto-conical recess 84 in the bottom of the die and has a stem 85 closely telescoped and splined in a hole in the bottom of the die cup 82 and an alined hole 86 in the inner part 87 of the die. The latter is a substantially solid plug which tapers downwardly and is seated in the complimental internal taper 88 of the outer part 82. The two parts are fastened together by screws 89 and a flange 80 on the part 87 is secured by screws 91 to a plate 90 having a lost motion connection later described with the movable ram 101 of the molding press.

7 To insure that the solidified plastic cup will always be withdrawn from the female die as the male die is raised to open the mold, part 64 (See FIG. 16) of the outer wall 64 of the male die, preferably near the upper end portion thereof, is formed with a radius somewhat larger than the part immediately below, the surface 64 flaring downwardly at an angle a. Thus, in the molding, an area 14" of the inner surface of the cup will be formed of reduced radius and therefore will interlock with the male die so that the cup will be fastened to this die as the latter is drawn upwardly (See FIGS. 9 and 10). The interference, however, is small enough to permit the cup wall 14 to be expanded and the cup stripped off easily from the retracted die by downward movement of the ejector head 83 relative to the die as illustrated in FIG. 11.

Provision is made in accordance with the present invention for lowering and raising the male die 63 in successive molding cycles, the lowering being sufficiently rapid and with enough propelling energy after impact by the male die with a molten glob in the female die to flatten the glob across the mold bottom, force the plastic upwardly through the thin side wall of the cavity 65, completely fill the thicker bead area 71, and force the volume excess outwardly between the surfaces 66, 67, all while the plastic is still molten and then hold the die closed for an interval long enough to insure complete solidification of the plastic before opening of the mold. While other types of quickly available energy sources may be employed, the necessary energy is derived in the present instance from a rotating flywheel 92 (FIG. 12) which, at proper times in the molding cycle, is coupled to and uncoupled from a shaft 93 whose undirectional motion may, through a suitable cam mechanism or, as in this instance, through cranks 94, be converted into lowering of the male die at least in the final closing of the mold in each cycle while dwelling the die in the closed position during cooling and final solidification of the plastic after complete filling of the mold cavity.

While the major parts of the downward closing and retracting motions of the male die may be effected by suitable hydraulically actuated mechanism and only the final closing movement produced by energy stored in the flywheel, the entire motion of the male die between the open (FIG. 12) and closed (FIG. 15) positions is derived from the flywheel by connecting the cranks 94 directly to the male die and providing crank throws of a length equal to the necessary stroke of the male die. For this purpose, the cranks are fast on axially alined parts of the shaft 93 journaled in bearings on a column 95 upstanding from a base structure 81. At their free ends, each crank is connected by an eccentric pin 96 on which is pivoted one end of an upright connecting rod 97, the lower end being connected through a suitable universal joint 98 with the upper end portion of the ram 101 whose outturned parallel edges 103 are slidable in vertical guides 102 (FIG. 14) on the column 95.

The lower end of the ram is secured by screws 104 (FIGS. 13 and 14) to a plate 105 which, for a purpose to appear later, is coupled through a spring loaded lost motion connection with the platen plate 90 to which the male die is clamped by the screws 91 (FIG. 15). The connection (See FIG. 14) includes a plurality of studs 106 angularly spaced around the mold axis and projecting upwardly and loosely through holes 107 in the plate 90 with their upper ends anchored at 108 in the bottom plate 105 of the ram. Springs 109 encircling the studs are compressed between the plate 90 and heads 111 on the studs thus acting to urge the platen upwardly against the end plate of the ram as shown in FIG. 14. The springs are, however, adapted to yield and allow the platen to remain separated from the plate 105 as shown in FIG. 13 in the initial upward movement of the ram as the cranks move beyond down dead center.

One of the shaft ends 93 carries the rotary element of an adequate friction brake indicated schematically at 111 (FIG. 12) and the driven disks of a similarly indicated clutch 112 having disks loose on the shaft and rotatable with the flywheel 92. External grooves in the periphery of the latter receive belts 113 which seat in a sheave 114 fast on the shaft of a driving motor 1 15. The clutch and brake are of the heavy duty type incorporating a suitable fluid pressure actuator which is energized to engage the clutch and release the brake in response to shifting of a valve 116 by energization of a solenoid 117. Springs associated with the actuator release the clutch and apply the brake when the solenoid is deenergized.

The actuating mechanism above described is typical of that commonly used in sheet metal stamping, the size and mass of the flywheel and the capacity of the clutch and brake being correlated with the energy required for the work to be done. So, in this instance, the flywheel is sized to store enough energy which, when applied to the plastic glob after engagement of the clutch and during the final movement of the crank to down dead center, will impart a sustained force sufficient to spread the molten plastic of the deposited glob into all parts of and completely fill the mold cavity. The energy required to accomplish the foregoing will depend, of course, on numerous factors including the volume of plastic required to form a cup of the desired size and shape, the viscosity of the molten plastic at the time of the impact, the wall thicknesses of the different parts of the cup, the temperatures of the mold walls, etc. All of these factors are considered in the design of the crank motion and the speed and mass of the flywheel.

The conventional crank actuated press above described is modified to provide, in accordance with the present invention, for dwelling of the male die 63 in its fully closed position (FIG. for a short interval, usually on the order of one or two seconds, sufficient to insure adequate cooling and complete solidification of the plastic after filling of the mold cavity. For this purpose, arcuate cams 118 (FIGS. 13,7 14, 22 and 23) are formed on or attached to the free ends of the cranks 94 with surfaces 130 during a substantial arc of movement of the cranks beginning at bottom dead center (FIGS. 14 and 22) engage rollers 119 on the upper ends of vertical follower rods 120 slidable in guides on the arms 121 projecting from brackets 122 which are secured to the column 95 on opposite sides of the connecting rod 97. Other parallel rods depending from the rod heads 123 are guided by the brackets to hold the follower rods against turning and position the followers 119 for proper engagement with the cams.

At their lower ends, the rods 120 bear against opposite ends of a bar 124 (FIGS. 13 and 14) extending crosswise of the ram through a cross slot 126 therein and secured to the rod ends by screws 125. The center of the bar 124 bears against the upper end of a tube 127 slidable in a bearing 128 in a central hole through the lower part of the ram 101. At its lower end, the tube bears against the top of the platen plate 90 to which the male die is secured as above described.

With the followers 119 thus connected to the platen 90 through abutment with the tube 127 and with the platen urged upwardly by the springs 109 to the normal positions shown in FIG. 14, the male die will move up and down with the ram while the cams 118 are out of engagement with the followers 119 as shown in FIG. 12. The cam surfaces 130 are concentric with the axis of the shaft 93 and disposed at a radius equal precisely to the throw of the cranks. As shown in FIG. 22, the leading end 131 of each surface comes into engagement with its follower roll 119just as the crank reaches bottom dead center. Then, in the continued turning of the cranks and so long as the surfaces remain in engagement with the followers, the male die will be held positively in fully closed position (FIG. 13) even though the crank continues on past dead center (FIG. 13) and initiates upward movement of the ram which thus becomes and remains separated from the platen 105. As the trailing ends 132 of the cams move past the followers, the platen rises under the force of the springs 109 and again comes into abutment with the bottom plate of the ram as shown in FIG. 14.

To continue such dwelling of the male die in fully closed position for an interval, for example, 2 seconds, long enough to insure complete solidification of the plastic filling the die cavity, provision is made for interrupting the drive to the cranks and actually stopping the crankshaft momentarily while the cam surfaces are still in engagement with the followers 119 as shown in FIG. 23. This is accomplished through a normally open switch 133 (FIG. 12) operating in conjunction with a time delay relay or timer 134 and in response to movement of the ram to control the energization of the solenoid 117 and in turn the activation and release of the clutch 112 and the brake 111 in timed relation to the crank motion. For this purpose, the switch may be actuated by a cam 135 on shaft 136 driven through a timing belt 143 from the crankshaft 93 so as to rotate in unison therewith. With the switch normally open, a relay 137 controlled thereby will be deenergized to hold a switch 138 closed, and the solenoid 117 energized from the power source 142. The valve 116 is thus positioned to cause the clutch to be engaged and the brake released. When the switch 133 is closed by the cam 135 as the crank reaches down dead center (FIG. 22) and at 140 (FIG. 24), the relay 137 will be energized to open the switch 138 and deenergize the solenoid thus effecting release of the clutch and application of the brake. After being uncoupled from the flywheel and a short angle of coasting, the cranks will stop at 143 with the cam surfaces 130 engaging the followers 119 as shown in FIG. 23 to hold the male die in fully closed position.

A timer sold by Giannini Controls Corp. as No. 241 is an example of a standard type adapted to be activated in response to closure of the switch 133 and operate after the expiration of the desired interval determined by an adjusting knob 141 to close a switch 142 and reenergize the solenoid 117. This shifts the valve 116 to cause the brake to be released and the clutch to be reengaged. The cranks are restarted but the cams 118 hold the mold closed until at 145, the trailing ends 312 pass the followers 119. Then, under the force of the springs 109, the male die and the platen are raised against the ram plate 105 as shown in FIG. 15 and then move upwardly with the ram.

SUPPORTING RELEASED CUP By virtue of the interlocking of the cup with the surface 64 of the die 63, the cup remains held by the die and moves upwardly with the same as shown in FIG. 9.

-12 and 14) which are moved inwardly across the lip of the female die after the bottom of the cup has been raised above such die lip. Herein there are two such supports in the form of bar-like fingers disposed in horizontal guides 146 (FIG. 14) formed in and extending radially across the top or the lip portion 61 of the female die 61 and slidable forth and back between a retracted position (FIGv out of the downward path of the male die and an advanced position (FIG. 10) in which the inner ends of the fingers project partially across the female die opening. The latter position is a short distance below the bottom of the cup held on the partially and upwardly retracted male die and ram.

The ends of the fingers outwardly beyond the die lip are pivotally connected at 147 to links 148 pivoted on the upper ends of the upstanding arms 149 of bellcranks fulcrurned at 150 on the lower die platen '79 and having outwardly projecting generally horizontal arms 151. The latter are continuously urged upwardly by compression springs 152 seated in the platen. Except during the uppermost and short part of each stroke of the ram, these springs are overcome and the bell-crank arms 151 are held depressed by stronger springs 153 encircling rods 154 and compressed between the underside of the die platen 105 and heads 155 rigid with the lower ends of the rods in vertical alinement with the free ends of the arms 151. TI'le rods 154 project slidably through holes in the lower ram plate 150 (See FIG. 1 1) and at their upper ends have heads 156 which are engaged by the plate 105 to time the extent of upward movement of ram before the springs 153 are overcome and the rods 154 raised to allow the springs 152 to act and project the fingers 145 inwardly into cup supporting position (FIG. 10). As shown in FIG. '24, the fingers are projected inwardly at 157 about the midpoint in the upward stroke of the ram and are retracted at 158 in the same part of the downstroke.

RELEASE OF CUP IN the upward movement of the ram by the crank and substantially simultaneously with the movement of the fingers 145 inwardly to the cup supporting position, the further upward movement of the ram is utilized to effect and time the separation of the cup ejector 83 and the male die and therefore the release of the cup ejector 83 and the male die and therefore the release of the cup from the male die. For this purpose, the stem 85 of the ejector, which forms the central part of the bottom surface of the male die as shown in FIG. 15, projects loosely up through the plates 90 and 105 and a hole 159 in the tube 127 above described. TI-Ie ejector is urged upwardly continuously be a spring 160 acting in compression between a shoulder 162 in the center hole of the male die and a collar 613 fixed to the rod. When the ejector is seated in the die 63 and the platen and die plates 90 and 105 are in abutment as shown in FIGS. 14 and 15, the upper end 164 of the stem 85 projects into the cross-slot 126 in the upper end of the hue 127 but somewhat short of a cross-bar 166 with which the stem' 85 is alined vertically. The bar is urged upwardly by the springs 169 and normally held against the bar 124 spanning the follower rods 120 (FIG. 14), the springs being compressed between the ends of the bar 166 and the ram plate 105.

At the proper time 171 (FIG. 24) in the upward movement of the ram and after the inward movement of the fingers to the cup supporting position, opposite ends of the bar 166 encounter the lower ends of rods 172 (FIG. 11) slidable vertically in hearings in brackets 173 fixed to the frame 95. These rods are urged downwardly by coiled compression springs 174 and are normally disposed as shown in FIG. 14 in a position determined by engagement of heads 175 with the upper ends of the bearing bushings 176. The ejector 83 remains seated in the die 63 until after the ends of the bar 166 have have encountered the spring loaded stops 172 and the ram and platen have moved upwardly enough further for the upper end 164 of the stem 85 to reach the bar 166 and be stopped thereby. Then, as the upward movement of the ram continues with the bar 166 thus blocked by a force determined by the springs 174, the upward movement of the ejector with the male die is interrupted in the continued upward movement of the ram, the male die will be separated from the ejector as shown in FIG. 11. This occurs at 171 shortly after the fingers 145 reach the cup supporting position. In the initial part of this movement, the cup is expanded by the cam action of the die surface 64 and thus tripped off from the die as the latter separated from the ejector. When the cup is fully released from the die, it falls (See FIG. 11) and comes to rest on the fingers 145.

REMOVAL OF MOLDED CUP After the lower end of the male die, as the crank approaches upper dead center (FIG. 12), rises above the lip 15 of the cup resting on the fingers, suitable means is rendered active to move the cup laterally off from the fingers and out of the molding press into a suitable collecting receptacle (not shown). Such bodily transfer is effected in the illustrated embodiment by directing a blast of air from a nozzle 178 against one side of the cup to apply a force sufficient to blow the cup laterally out of the molding press. To this end, compressed air from a source 179 is admitted momentarily to the nozzle through a valve 180 (FIG. 12) which is opened by energization of a solenoid 181 in response to momentary closure of a switch 182 by a cam 183 on the shaft 136. The blast, which occurs at 184 (FIG. 24) is thus timed precisely with the molding cycle so that the finished cup is moved out of the way by the time 185 that the next glob 11 is propelled from the nozzle 49 and enters the female die recess preparatory of the next molding cycle.

COOLING OF CAVITY WALLS In accordance with another aspect of the invention, provision is made for maintaining the walls of the die cavity at temperatures which are considerably lower than that of the molten plastic as the cavity becomes filled thus accelerating solidification of the plastic and shortening the overall cycle without, however, precluding complete filling of the cavity including the bead area 71 and partial filling of the overflow space 72. For this purpose, a body of liquid such as water in a tank 186 (FIG. 17) is maintained at a proper temperature and circulated continuously as by a power driven pump 187 through grooves 188 and 189 embedded in and spiraled around and along the dies 61 and 63 adjacent the walls 62 and 64 which define the cavity 65. The

proper temperature which may vary substantially with different kinds of plastics, time of operation of the molding press, size of the cup, etc., is determined by the setting of a thermostat 191 which regulates the effectiveness of suitable cooling and heating exchangers immersed in the tank water. Herein, the groove 188 is a helix formed around the exterior of the part 73 of the female die and extends over the full depth of the cavity sidewall from an inlet 192 near the lip of the cavity to an outlet 193 near the bottom of the die at about the level of the cavity bottom. The water enters the inlet 192 from an annular groove 194 somewhat deeper than the groove of the helix and disposed in a plane just below the bead and overflow area 70 of the cavity. On the side diametrically opposite from the inlet 192, the groove communicates at 195 with the supply pipe 196 from the pump 187 so that the incoming water flows around the short are of the groove to direct the incoming water around the full circumference of the groove before entering the spiral at 192.

In a similar way, tempered water from the tank is forced through a flexible hose 197 (FIG. 17-) extending into and through the flange 80 of the male die and, through an inlet 198, enters on one side of an annular horizontal groove 199 disposed a little above the level of the cup lip. On the opposite side of the groove and at 201, the water enters the upper end of a downwardly spiraled groove 202 which is formed in the inner die part 87 and tapers downwardly so as to be spaced equidistantly from the side wall of the mold cavity. At the lower end, the spiral communicates with a passage 203 extending upwardly through the part 87 to an outlet at the inner end of a hose 204 by which the water is returned to the tank. The hoses are made flexible so as to accommodate the up and down movements of the male die in each molding cycle.

With the water passages arranged as above described within the male and female dies, the thin side wall and walls of the bead area 71 of the cavity 65 will be maintained at temperatures which, at the upper ends of the cavity, approximate the temperature maintained in the tank. Then, by the absorption of heat from the warmer plastic in accelerating solidification thereof, the temperature of the cavity walls will decrease progressively and downwardly to near the bottom of the cavity. It has been found that by downward conduction through the bottom portion of the mold, the bottom walls of the cavity 65 will, for most containers for about one pound of most food products, be maintained at the proper temperatures without the necessity of extending the cooling water passages into these areas. For containers of larger diameter or those having a bottom wall substantially thicker than the side wall, it may be desirable to provide for cooling the bottom of the female die or the extreme lower end of the male die.

The temperature of the cooling liquid most effective for causing and properly timing the solidification of the plastic in all parts of the cavity substantially simultaneously will vary somewhat during operation of the molding press from a cold start. Thus, it may be desirable to provide a higher water temperature in the initial operation and schedule the decrease in the temperature according to the time required for equilibrium conditions to be attained. Of course, the design of the proper cooling system will be influenced by numerous factors including the kind and softening point of the plastic being used, the size and depth of the container being molded, the wall thicknesses of different parts thereof, the frequency of the molding cycles, the lengths of the dwell intervals, and the excess plastic required to insure formation of a complete flash ring 72. The prime objective is to avoid such cooling of the plastic in any part of the cavity that would produce an objectionable reduction in the desired high flow velocity all the way to and through the enlarged bead area 71 which is beyond the most restricted cross-section of the cavity side wall.

On the other hand, it is desirable, in order to insure complete solidification of the plastic as soon as possible after the mold has been tilled and the flash ring 72 formed, thereby providing a molding cycle of overall minimum length. By properly correlating the cooling with various factors involved, it has been possible to produce cups of the construction disclosed in molding press cycles of the above character less than one third of the time that would be required in conventional injection molding following most improved techniques.

In the molding of some cups in accordance with the present invention, particularly cups of larger than the conventional one pound size, it may be desirable in order to minimize the pressure developed in the bottom of the mold cavity, to provide for the escape of some of the excess of the plastic of the glob after complete filling of the cavity and some overflowing from the bead area 71. For this purpose, a small hole 220 (FIG. 15), for example 0.015 inches in diameter, may be formed in the bottom of the female die 61, such hole being relatively short and communicating with a passage 221 of larger cross-section open at its lower end. Any plastic forced into and through the restriction 210 will be forced downwardly and disposed of in the next molding cycle.

SUMMARY OF OPERATION AND ADVANTAGES OF THE APPARATUS(FIGS. 1 TO 26) Each cycle of the molding press comprising in this instance one revolution of the crank shaft 93 will be executed in two or three seconds, one of the cups 11 being produced in each cycle.

While the crank is passing top dead center (FIG. 12) and the male die is retracted above the female die, the plunger 48 will be advanced rapidly by its actuator 51, 52 to the position shown in FIG. 21 thus cutting off a predetermined length of plastic from the leading end of the stream 24 and propel a uniformly heated glob 10 horizontally partially across the open top of the female die as shown in phantom in FIG. 4 by the time that the male die starts downwardly. As the glob falls into the die, lowering of the male die 63 is initiated so that as the glob reaches the bottom of the die 61, it is engaged substantially immediately by the lower end of the die as shown in full in FIG. 4, then in the lower part of its downstroke.

Under the impact propelled by the ample energy stored in and derived from the flywheel, the glob is flattened against the bottom of the female die and forced to flow laterally in all directions across the bottom wall. The plastic mass is thus formed into a relatively thick wafer 204 (FIG. 5) which decreases in thickness and increases in diameter as the male die advances and before substantial cooling of the mass. Because of the substantially lesser cross-sectional area of the side wall of the cavity 65 at this time, the lateral flow outwardly across the bottom of the cavity continues until the full area has been covered including filling of the pedestal area 205. Then, under the continues downwardly applied propelling force, upward flow of the plastic into the lower end of the cavity sidewall 206 is initiated. As illustrated in FIG. 6, the rate of upward flow along different parts of this wall may vary die to slight variations in the wall thickness of the cavity. Thus, the plastic on one side may reach the bead area 71 before that on the other side as illustrated in FIG. 7. Owing, however, to the restriction due to the close spacing of the surfaces 66, 67, as the male die comes close to its lowermost position (FIG. 8), escape of the plastic fromv the die cavity will be precluded until after the area 71 of the cavity has been filled completely. After such filling and, in the final downward movement of the die, the excess of the original glob volume will be forced out of the bead area 71 around the full circumference of the latter and through the narrow gap between the surfaces 66, 67. Thus, a thin and circumferentially continuous flash fin 207 (FIG. 18) will be left around the outermost edge of the head 15 in the cup as molded. The remainder of the glob volume will flow past the narrow gap 66, 67 and into the surrounding area 70 forming thickened arcuate segments 208 (FIG. 18) which may be separated angularly from each other but usually will form a continuous thickened annulus of plastic and varying cross-section integral with the outer edge of the fin 207.

As the crank reaches bottom dead center (FIG. 22), the leading ends 131 of the cams 118, the switch 133 will be closed to start the timer 134 and cause release of the clutch I12 and the application of the brake 111 as above described. The crank is stopped somewhat beyond dead center (FIG. 23) with the cam surfaces 130 engaging the followers 119 which act through the rods 120 to hold the male die in the fully closed position (FIG. 15). The ensuing short dwell determined by the timer is sufficient to cause complete solidification of all of the plastic in contact with the substantially cooler cavity walls.

At the end of the selected dwell period, the timer causes release of the brake and reengagement of the clutch so that turning of the crank from the position shown in FIG. 24 is resumed. Upward retraction of the male die starts as the trailing cam ends 132 pass the followers 119, the molded cup being held on the die as shown in FIG. 9.

When the cup has been raised above the top of the female die, the fingers 145 are projected into supporting position beneath the cup bottom as shown in FIG. 10. Then, as the die continues upwardly, the cross-bar 166 is blocked by the rods 172 (FIG. 11, the ejector 83 and the cup bottom being held against further upward movement with the die. The upper part of the cup is thus expanded as the die surface 64" is withdrawn therefrom in the continued upwardly movement of the die, the cup dropping onto the fingers 145 as shown in FIG. 11 as soon as it is freed from the die.

Finally, and when the crank nears top dead center, the lower end of the male die and the projecting ejector will be disposed above the level of the cup lip as shown in FIG. 12. At this time, a blast of air from the nozzle 178 is directed against the side of the cup in a direction transversely of or away from the glob discharge nozzle 47 so as to below the cup laterally and off from the supporting fingers 145 and away from the dies to a collecting receptacle.

With the finished cup moved out of the way, the mold, as the crank passes through top dead center, holds open long enough to the next glob 10 of plastic discharged from the nozzle 47 to be received in the female die. Another cycle of the molding press is thus initiated immediately without interrupting the drive to the crank.

Because of the thinness and more or less frangible character of the fin 207 connected the bead 15 and the irregular annulus 208 (FIG. 19), the composite ring 72 formed thereby may easily be broken away from the bead. Such braking may take place automatically during removal of the finished cup from the dies by the air blast from the nozzle 178 or during falling of the cup in a collecting receptacle. Alternatively, positive separation of the cup from the flash ring may be effected in a simple trimming operation involving pressing the finally molded cup through a hole equal in diameter to the outside diameter of the cup bead 15.

The apparatus above described may also be used in the formation of other cup-like articles such as the overcap 210 shown in FIG. 25 which comprises a thin flat bottom, concentric cylindrical tubes 211 and 213 integral with and upstanding from the bottom, and cylindrical side walls 211 and 214 terminating in lip ends 212 and 215. The male female dies for molding the cap are shown in FIG. 26 in a diametrical section comparable to FIG. 15, the corresponding parts being indicated by the same but primed reference numerals. In this instance, the female and male dies 61' and 63 telescope together at 216 in the closed position of the mold in order to form the lip 212. The cavity for forming the upper end portion of the inner tube 214 is formed within the inner part of the male die 63'. The plastic of the glob in excess of that required to fill the die cavity as shown escapes through a restriction in the form of a small hole 223 in the ejector 83' communicating with an open passage 224 extending upwardly through the stem 85.

MODIFICATION FIGS. 27 TO 34 It sometimes happens in the apparatus shown in FIGS. 1 to 26 that the plastic glob comes to rest in a position offset somewhat laterally from the center of the bottom of the mold cavity, this condition being conducive to unequal lateral and upward flow of the plastic in the mold cavity. To overcome this, the present invention, in another aspect, contemplates the provision of means for injecting the molten plastic forming each successive one of the globs 10 into the bottom of the mold cavity through a passage extending generally axially through the stationary one of the dies, such injection being effected by a power actuated plunger whose head end becomes a part of the stationary die and is flush with the end wall thereof during the final closing of the mold.

This improvement is illustrated schematically in FIGS. 27 through 34 in which the parts in common with those above described are indicated by the same reference numerals. Even though shown schematically, 

1. Apparatus for converting globs of thermoplastic into cups and the like having, in combination, a mold having male and female dies adapted, when closed in telescoped relation, to define a closed cavity having a generally flat bottom and an upstanding peripheral side wall of a combined volume at leasT equal to that of the bottom and side wall of each cup to be formed, means supporting said dies for relative movement between an open position and said closed position, mechanism operable in repeated cycles to move said dies axially relative to each other and back and forth to open and close said mold, means for continuously heating and melting a mass of thermoplastic while confining and pressurizing the same to form a stream advancing toward said dies, means operating in each of said cycles to cut off a length of predetermined volume from the leading end of said molten stream and discharge the glob thus formed substantially simultaneously with the cut-off and without substantial loss in temperature into said mold between the opposed bottom walls of said male and female dies while such walls are separated, said predetermined volume of the glob of molten plastic being at least equal to the total volume of said cavity, power driven means actuating said mechanism in each of said cycles during each of which the mold is opened, then fully closed immediately after receiving said molten glob, and finally held closed long enough to allow the molten plastic to solidify after compression thereof in and complete filling of said cavity, said actuating means acting immediately upon the delivery of one of said globs into said cavity to close the mold with sufficient rapidity and with enough propelling energy in the final closing to force the plastic of the still molten glob to flow laterally across the bottom of said cavity and then upwardly through the side wall thereof so as to fill the bottom and side wall of the cavity completely before substantial cooling and solidification of the plastic, said cut-off means including a passage disposed within and extending along the axis of said stationary die to and through the end wall thereof and opening into said cavity at the center of such end, a plunger reciprocable back and forth in and along such passage between a retracted position and an advanced position in which the leading and head end of the plunger is substantially flush with the surrounding wall of said stationary die so as to form the central part of such wall during final closing of the mold, power actuated means for forcing one of said globs of said molten plastic into said passage ahead of said plunger while the latter is in said retracted position, a power actuator operated in timed relation to the opening and closing of said mold to advance said plunger and discharge the plastic glob into the center of said cavity while the opposed end walls thereof are spaced apart and the mold is partially open, and means holding said plunger in said advanced position during the ensuing closure of the mold by said power driven means.
 2. Apparatus as defined in claim 1 in which said holding means includes a member mounted on said stationary die for movement transversely of said plunger into and out of the path of retraction of the plunger whereby to positively block the plunger against retraction from said flush position during the final closing of the mold.
 3. Apparatus as defined in claim 1 in which the start of the injection of said glob into said mold cavity occurs while the male and female dies are partially telescoped together and the end walls thereof are approaching final mold closed positions whereby the collapsing of the glob and flow of its plastic laterally and outwardly across said end walls occurs substantially simultaneously with the completion of the injection of the glob into the mold cavity.
 4. Apparatus as defined in claim 3 including a second passage extending transversely of said first passage and communicating with the latter adjacent and ahead of the leading end of said plunger when the latter is in said retracted position, a third passage confining the leading end portion of said advancing stream of pressurized molten plastic and communicating with said second passage at a point spaced from said second passage, a plunger slidable back and forth in said second passagE between a retracted position uncovering the leading end of said third passage and an advanced position covering such end whereby to admit molten plastic from said third passage into said second passage and then, during advance of the plunger to cut off the advanced end of said stream and force the resulting glob into said first passage, while the first plunger is retracted, and power actuated means operating in timed relation to the movement of said first plunger to advance said second plunger after a predetermined volume of the plastic has been admitted to the second passage, the leading and head end of said second plunger being disposed closely adjacent said first passage in the advanced position of the second plunger. 